1. Field of the Invention
The present invention relates to a method of manufacturing a pleated multilayer bag having an inner layer formed of a tubular synthetic resinous film.
2. Background of the Prior Art
A method of a pleated multilayer bag is known from Japanese Patent Publication No. 58-52834, in which opposite side edges of a tubular plastic film are wrapped up by an outer-layer bag material, while the outer-layer bag material and the pleats of the tubular plastic film are superimposed upon each other in a close contact relationship.
Further, a method is also known from Japanese Patent Publication No. 46-1749, in which a periphery of an inner plastic layer is wrapped up by an outer paper layer, while gores are formed on both sides of the outer paper layer and the inner plastic layer.
In the method disclosed in the above Japanese Patent Publication No. 48-52834, the tubular plastic film is drawn into a rectangular cross-sectional tube forming device comprising an outer group of rolls and an inner group of rolls, in such a manner that the inner group of rolls are arranged within the tubular plastic film. A lower side of the outer-layer bag material superimposed upon a lower side of the tubular plastic film is caused to pass, together with a lower portion of the tubular plastic film, through a nip between a lower roll of the outer group of rolls and a lower roll of the inner group of rolls. The tubular plastic film is further drawn into the forming device while the opposite side edges of the outer-layer bag material are covered by upper rolls of the outer group of rolls to form pleats on the opposite side walls of the multilayer rectangular cross-sectional tube. Thus, the rectangular tube forming device is required for the method of the above Japanese patent, in order to form the tubular plastic film into the rectangular cross-sectional tube. Accordingly, the arrangement for carrying out the method is complicated in construction. Further, when the tubular plastic film is formed into the rectangular cross-sectional tube by the rectangular tube forming device, dust, various germs and the like are penetrated together with air into the tubular plastic film, causing a sanitary problem.
In the method disclosed in the above Japanese Patent Publication No. 46-1749, rotating air-needles are provided to form perforations in the inner plastic layer of the multilayer bag in a periodical manner from the outside, and air is supplied through the perforations to inflate the inner plastic layer. Thus, the air-needle, a gas supply mechanism and the like for supplying the air into the inner plastic layer are required for the arrangement for carrying out the method. Accordingly, the arrangement is complicated in construction. Moreover, there is such a concern that the dust, various germs or the like will penetrate together with air into the tubular plastic film, causing a sanitary problem.